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排序方式: 共有163条查询结果,搜索用时 453 毫秒
111.
Drinking water production by ultrafiltration of Songhuajiang River
with PAC adsorption 总被引:1,自引:0,他引:1
In recent years, membrane ultrafiltration (UF) of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m^2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon (PAC) adsorption. Turbidity was almost completely removed to less than 0.2 NTU (below Chinese standard 1 NTU). It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn, 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30. 相似文献
112.
Janine M. Castro Philip L. Jackson 《Journal of the American Water Resources Association》2001,37(5):1249-1262
ABSTRACT: The model bankfull discharge recurrence interval (annual series) (Ta) in streams has been approximated at a 1.5‐year flow event. This study tests the linkage between regional factors (climate, physiography, and ecoregion) and the frequency of bank‐full discharge events in the Pacific Northwest (PNW). Patterns of Ta were found to be significant when stratified by EPA Ecoregion. The mean value for Ta in the PNW is 1.4 years; however, when the data is stratified by ecoregion, the humid areas of western Oregon and Washington have a mean value of 1.2 years, while the dryer areas of Idaho and eastern Oregon and Washington have a mean value of 1.4 to 1.5 years. Among the four factors evaluated, vegetation association and average annual precipitation are the primary factors related to channel form and Ta. Based on the results of the Ta analyses, regional hydraulic geometry relationships of streams were developed for the PNW, which relate variables, such as bank‐full cross‐sectional area, width, depth, and velocity, to bankfull discharge and drainage area. The verification of Ta values, combined with the development of regional hydraulic geometry relationships, provides geographically relevant information that will result in more accurate estimates of hydraulic geometry variables in the PNW. 相似文献
113.
对于高度非线性的城市污水处理厂区间数优化设计模型(IPODM),若采用传统的方法求解,不仅计算繁琐,且难以有效地寻找全局最优解.本文通过引入遗传算法(GA),与传统的步长搜索法相结合,大大提高了问题的求解效率.本文给出了这种改进算法在某一城市污水处理厂优化设计中的应用实例.结果表明,不仅解的搜索效率有明显的提高,而且目标函数值在原有的基础上改进了20%,有着显著的经济效益;但是由于遗传算法自身的局限性,所求得的解只是一定条件下的最优区间解. 相似文献
114.
Petrochemical plants and refineries consist of hundreds of pieces of complex equipment and machinery that run under rigorous operating conditions and are subjected to deterioration over time due to aging, wear, corrosion, erosion, fatigue and other reasons. These devices operate under extreme operating pressures and temperatures, and any failure may result in huge financial consequences for the operating company. To minimize the risk and to maintain operational reliability and availability, companies adopt various maintenance strategies. Shutdown or turnaround maintenance is one such strategy. In general, shutdown for inspection and maintenance is based on the original equipment manufacturer's (OEM) suggested recommended periods. However, this may not be the most optimum strategy given that operating conditions may vary significantly from company to company.The framework proposed in this work estimates the risk-based shutdown interval for inspection and maintenance. It provides a tool for maintenance planning and decision making by considering the probability of the equipment or system for failure and the likely consequences that may follow. The novel risk-based approach is compared with the conventional fixed interval approach. This former approach, characterized as it is by optimized inspection, maintenance and risk management, leads to extended intervals between shutdowns. The result is the increase in production and the consequent income of millions of dollars.The proposed framework is a cost effective way to minimize the overall financial risk for asset inspection and maintenance while fulfilling safety and availability requirements. 相似文献
115.
以两组典型毒性数据为例,综合比较了5种常见概率单位模型计算程序在EC50估算上的差异,并在此基础上比较了3种不同置信区间的估算方法.在对照组受抑制率为零时,5种方法的参数估算结果一致;当对照组受抑制率不为零时,将对照组数据纳入整个计算过程的方法可以给出可靠的参数估算结果.3种不同置信区间估算方法的比较表明:在毒性数据分布对称性良好的情况下,基于Delta函数与Fieller定理的方法给出的结果相近,但后者可以在更广泛的情况下给出置信区间;相比而言,基于bootstrap重抽样的非参数方法获得的置信区间较窄,表现出更好的灵敏度. 相似文献
116.
为解决故障电弧断路器动作响应滞后、效率低等问题,基于电气火灾多发原因与防控实验装置、功率因素可调式负载柜,搭建故障电弧模拟实验台,研究故障电弧断路器响应时间影响因素,利用功率分析仪统计断路器响应时间。研究结果表明:纯电阻电路中,断路器响应时间随碳电极直径增大而缩短;在负载功率P=800,2 000 W条件下,碳电极直径D≥2 mm时,断路器瞬时保护率达100%;负载功率P=3 200 W时,断路器瞬时保护率小于50%;碳电极直径D为1,2 mm时,断路器最佳负载功率保护区间分别为[1 200,1 600] W,[800,2 400] W,碳电极直径为2 mm的保护区间范围较宽,安全可靠性更高;感性电路中,断路器响应时间随功率因数减小而延迟,功率因数对断路器动作响应时间的影响随负载功率增加而降低。研究结果可为故障电弧断路器响应时间的设定提供参考。 相似文献
117.
为了能够对煤矿采空区遗煤自燃危险性进行准确判定,提出基于IIAHP-Entropy-ssd最优综合赋权模糊评价模型。首先,结合影响采空区遗煤的自燃性及环境影响因素,建立危险性评价指标体系,并确定各评价指标的分级准则;其次,利用区间数代替数值评价打分,并运用可能度互补矩阵进行修正的改进区间数层次分析法(IIAHP),结合熵权法(Entropy),根据现场实测数据,得出各评价指标的主、客观权重,并运用离差平方和(ssd)的最大化思想进行最优综合赋权,克服评价过程中主、客观因素对评价结果的影响,运用属性数学理论,建立各评价指标的隶属函数;最后,运用该模型对忻州窑矿8914综放工作面采空区遗煤自燃危险性进行评价,并与现场实际情况进行对比,结果表明:该模型的评价结果与实际情况基本一致,验证了该评价模型的准确性,为采空区遗煤自燃危险性评价提供参考和借鉴思路。 相似文献
118.
In incremental eco-design improvements, design engineers attempt to modify an existing product via some eco-design measures to reduce the product’s environmental impacts (e.g. reduction of material usage and energy consumption). In this process, several design concepts can be proposed, and concept selection is required to allocate resources sensibly to promising design concepts only. In this context, the research purpose is to estimate the environmental impacts of each concept given the uncertainty of design information. In the proposed methodology, the fuzzy interval arithmetic is used to specify and propagate imprecise design information. Then, the centroid concept is applied to model different views of imprecision (i.e. pessimistic, balanced and optimistic) associated with fuzzy impact assessment. Accordingly, a decision scheme is developed to support concept selection and suggest the potential areas for further eco-design improvements. A coffee maker is used as an example to demonstrate the proposed methodology. Also, the Monte Carlo Simulation is applied for the same example to compare the numerical outcomes by the fuzzy interval approach. 相似文献
119.
120.